Production of olefins from biorenewable feedstocks

ABSTRACT

A process for producing olefins from a feedstock comprising a petroleum and non-petroleum fraction has been developed. The process comprises first pretreating the feedstock to remove contaminants such as alkali metals and then cracking the purified feedstock in a fluidized catalytic cracking (FCC) zone operated at conditions to provide C 2 -C 5  olefins. Alternatively, the non-petroleum fraction can first be treated and then mixed with petroleum fraction to provide the feedstock which is then catalytically cracked.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part of application Ser. No.11/432,012 filed May 11, 2006, now U.S Pat. No. 7,288,685, which in turnclaims priority from Application Ser. No. 60/682,722 filed May 19, 2005now abandoned, both of which are hereby incorporated by reference intheir entirety.

FIELD OF THE INVENTION

This invention relates to a process for converting a feedstockcomprising a petroleum and non-petroleum fraction to olefins. Examplesof non-petroleum fractions are vegetable oils and used greases. Theprocess involves first pre-treating the feedstock to remove contaminantssuch as alkali metals and then catalytically cracking the purifiedfeedstock to provide a product stream comprising C₂-C₅ olefins.

BACKGROUND OF THE INVENTION

Fluid Catalytic Cracking (FCC) is one method which is used to produceolefins, especially propylene, from heavy crude fractions. There arereports in the literature that vegetable oils such as canola oil couldbe processed using FCC to give a hydrocarbon stream useful as a gasolinefuel.

Applicants have developed a process which successfully converts afeedstock comprising a petroleum and a non-petroleum fraction, e.g.vegetable oils and greases, to C₂-C₅ olefins. The process involves firstremoving contaminants such as alkali metals and then taking the purifiedfeedstock, flowing it through an FCC zone and collecting a productstream comprising olefins.

SUMMARY OF THE INVENTION

One embodiment of the invention is a process for the catalytic crackingof a feedstock comprising a petroleum fraction and a non-petroleumfraction comprising first treating the feedstock in a pretreatment zoneat pretreatment conditions to remove at least a portion of portion ofcontaminants present in the feedstock and produce an effluent stream;flowing the effluent from the pretreatment zone to a fluid catalyticcracking zone where the effluent is contacted with a cracking catalystat cracking conditions to provide a product stream comprising C₂-C₅olefins and hydrocarbons wherein the pretreatment step is selected fromthe group consisting of contacting the feedstock with an acidic ionexchange resin or contacting the feedstock with an acid solution.

In another embodiment, the non-petroleum fraction is first treated toremove contaminants and then mixed with the petroleum fraction toprovide the feedstock.

This and other objects and embodiments will become clearer after thefollowing detailed description of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The feedstock which is used in the current process comprises a petroleumfraction and a non-petroleum fraction. The petroleum fraction can be anyof those hydrocarbon streams which are routinely processed usingfluidized catalytic cracking (FCC) technology and which are known in theart. The non-petroleum fraction includes fractions or feedstocks otherthan those obtained from crude oil. One example of a non-petroleumfraction is a biorenewable feedstock which comprise tri-glycerides andfree fatty acids (FFA). Examples of these feedstocks include, but arenot limited to, canola oil, corn oil, soy oils, rapeseed oil, soybeanoil, colza oil, sunflower oil, hempseed oil, olive oil, linseed oil,coconut oil, castor oil, peanut oil, palm oil, mustard oil, cotton seedoil, inedible tallow, inedible oils, e.g. jatropha oil, yellow and browngreases, lard, train oil, fats in milk, fish oil, algal oil, tall oil,sewage sludge and the like. Tall oil is a by-product of the woodprocessing industry. Tall oil contains esters and rosin acids inaddition to FFAs. Rosin acids are cyclic carboxylic acids. Thetriglycerides and FFAs of the typical vegetable or animal fat containaliphatic hydrocarbon chains in their structure which have about 8 toabout 24 carbon atoms. Pyrolysis oils, which are formed by the pyrolysisof cellulosic waste material can also be used as a non-petroleumfeedstock or a portion of the feedstock. Other non-petroleum feedstockcomponents include oxygenated liquids derived from gasification of coalor natural gas followed by a downstream liquefaction step such asFischer-Tropsch technology or alcohol synthesis; oxygenated liquidsderived from depolymerization, thermal or chemical, of waste plasticssuch as polypropylene, high density plastics such as polypropylene, highdensity polyethylene, and low density polyethylene; and other syntheticoils generated as byproducts from petrochemical and chemical processes.Mixtures of the above feedstocks may also be used.

However, these non-petroleum feedstocks also contain contaminants suchas alkali metals, e.g. sodium and potassium, phosphorous as well as ash,water and detergents. Accordingly, the first step in the presentinvention is to remove as much of these contaminants as possible. Onepretreatment step involves contacting the non-petroleum feedstock withan ion-exchange resin in a pretreatment zone at pretreatment conditions.The ion-exchange resin is an acidic ion exchange resin such asAmberlyst™-15 and can be used as a bed in a reactor through which thefeedstock is flowed through, either upflow or downflow. The conditionsat which the reactor is operated are well known in the art.

Another means for removing contaminants is a mild acid wash. This iscarried out by contacting the feedstock with an acid such as sulfuric,acetic, nitric or hydrochloric acid in a reactor. The acid and feedstockcan be contacted either in a batch or continuous process. Contacting isdone with a dilute acid solution usually at ambient temperature andatmospheric pressure. If the contacting is done in a continuous manner,it is usually done in a counter current manner.

Yet another means of removing metal contaminants from the feedstock isthrough the use of guard beds which are well known in the art. These caninclude alumina guard beds either with or without demetallationcatalysts such as nickel or cobalt.

Since only the non-petroleum fraction needs to be pretreated, theeffluent from the pretreatment zone is now mixed with the petroleumfraction to provide a feedstock mixture which is now flowed to an FCCzone. Alternatively, the petroleum and non-petroleum fractions can befirst mixed and then treated in a pretreatment zone as described above.Which method is used depends on the overall setup in any one refinery.In the FCC zone the hydrocarbonaceous components are cracked to olefins.Catalytic cracking is accomplished by contacting hydrocarbons in areaction zone with a catalyst composed of finely divided particulatematerial. The reaction is catalytic cracking, as opposed tohydrocracking, and is carried out in the absence of added hydrogen orthe consumption of hydrogen. As the cracking reaction proceeds,substantial amounts of coke are deposited on the catalyst. The catalystis regenerated at high temperatures by burning coke from the catalyst ina regeneration zone. Coke-containing catalyst, Coke-containing catalyst,referred to herein as “coked catalyst”, is continually transported fromthe reaction zone to the regeneration zone to be regenerated andreplaced by essentially coke-free regenerated catalyst from theregeneration zone. Fluidization of the catalyst particles by variousgaseous streams allows the transport of catalyst between the reactionzone and regeneration zone. Methods for cracking hydrocarbons in afluidized stream of catalyst, transporting catalyst between reaction andregeneration zones, and combusting coke in the regenerator are wellknown by those skilled in the art of FCC processes.

An arrangement which can make up the FCC zone of the present inventionis shown in U.S. Pat. No. 6,538,169 which is incorporated in itsentirety by reference and comprises a separator vessel, a regenerator, ablending vessel and a vertical riser that provides a pneumaticconveyance zone in which conversion takes place. The catalysts which canbe used in the present process are any of those well known in the artand comprises two components that may or may not be on the same matrix.The two components are circulated throughout the entire system. Thefirst component may include any of the well-known catalysts that areused in the art of fluidized catalytic cracking, such as an activeamorphous clay-type catalyst and/or a high activity, crystallinemolecular sieve. Molecular sieve catalysts are preferred over amorphouscatalysts because of their much-improved selectivity to desiredproducts. Zeolites are the most commonly used molecular sieves in FCCprocesses. Preferably, the first catalyst component comprises a largepore zeolite, such as a Y-type zeolite, an active alumina material, abinder material, comprising either silica or alumina and an inert fillersuch as kaolin.

The zeolitic molecular sieves appropriate for the first catalystcomponent should have a large average pore size. Typically, molecularsieves with a large pore size have pores with openings of greater than0.7 nm in effective diameter defined by greater than 10 and typically 12membered rings. Pore Size Indices of large pores are above about 31.Suitable large pore zeolite components include synthetic zeolites suchas X-type and Y-type zeolites, mordenite and faujasite. We have foundthat Y zeolites with low rare earth content are preferred in the firstcatalyst component. Low rare earth content denotes less than or equal toabout 1.0 wt-% rare earth oxide on the zeolite portion of the catalyst.Octacat™ catalyst made by W.R. Grace & Co. is a suitable low rare earthY-zeolite catalyst.

The second catalyst component comprises a catalyst containing, mediumpore zeolites exemplified by ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35,ZSM-38, ZSM-48, and other similar materials. U.S. Pat. No. 3,702,886describes ZSM-5. Other suitable medium pore zeolites include ferrierite,erionite, and ST-5, developed by Petroleos de Venezuela, S.A. The secondcatalyst component preferably disperses the medium pore zeolite on amatrix comprising a binder material such as silica or alumina and aninert filler material such as kaolin. The second component may alsocomprise some other active material such as Beta zeolite. These catalystcompositions have a crystalline zeolite content of 10 to 25 wt-% or moreand a matrix material content of 75 to 90 wt-%. Catalysts containing 25wt-% crystalline zeolite material are preferred. Catalysts with greatercrystalline zeolite content may be used, provided they have satisfactoryattrition resistance. Medium pore zeolites are characterized by havingan effective pore opening diameter of less than or equal to 0.7 nm,rings of 10 or fewer members and a Pore Size Index of less than 31.

The total catalyst composition should contain 1 to 10 wt-% of a mediumpore zeolite with greater than or equal to 1.75 wt-% being preferred.When the second catalyst component contains 25 wt-% crystalline zeolite,the composition contains 4 to 40 wt-% of the second catalyst componentwith a preferred content of greater than or equal to 7 wt-%. ZSM-5 andST-5 type zeolites are particularly preferred since their high cokeresistivity will tend to preserve active cracking sites as the catalystcomposition makes multiple passes through the riser, thereby maintainingoverall activity. The first catalyst component will comprise the balanceof the catalyst composition. The relative proportions of the first andsecond components in the catalyst composition will not substantiallyvary throughout the FCC unit.

The high concentration of the medium pore zeolite in the secondcomponent of the catalyst composition improves selectivity to lightolefins by further cracking the lighter naphtha range molecules. But atthe same time, the resulting smaller concentration of the first catalystcomponent still exhibits sufficient activity to maintain conversion ofthe heavier feed molecules to a reasonably high level.

Cracking of the feedstock takes place in the riser section of the FCCzone. Feed is introduced into the riser by a nozzle resulting in therapid vaporization of the feed. Before contacting the catalyst, the feedwill ordinarily have a temperature of about 149° C. to about 316° C.(300° F. to 600° F.). The catalyst is flowed from a blending vessel tothe riser where it contacts the contacts the feed for a time of about 2seconds or less.

The blended catalyst and reacted feed vapors are then discharged fromthe top of the riser through an outlet and separated into a crackedproduct vapor stream including olefins and a collection of catalystparticles covered with substantial quantities of coke and generallyreferred to as “coked catalyst.” In an effort to minimize the contacttime of the feed and the catalyst which may promote further conversionof desired products to undesirable other products, any arrangement ofseparators such as a swirl arm arrangement can be used to remove cokedcatalyst from the product stream quickly. The separator, e.g. swirl armseparator, is located in an upper portion of a chamber with a strippingzone situated in the lower portion of the chamber. Catalyst separated bythe swirl arm arrangement drops down into the stripping zone. Thecracked product vapor stream comprising cracked hydrocarbons includinglight olefins and some catalyst exit the chamber via a conduit which isin communication with cyclones. The cyclones remove remaining catalystparticles from the product vapor stream to reduce particleconcentrations to very low levels. The product vapor stream then exitsthe top of the separating vessel. Catalyst separated by the cyclones isreturned to the separating vessel and then to the stripping zone. Thestripping zone removes adsorbed hydrocarbons from the surface of thecatalyst by counter-current contact with steam.

A first portion of the coked catalyst is recycled to the riser withoutfirst undergoing regeneration. A second portion of the coked catalyst isregenerated in the regenerator before it is delivered to the riser. Thefirst and second portions of the catalyst may be blended in a blendingvessel before introduction to the riser. The recycled catalyst portionmay be withdrawn from the stripping zone for transfer to the blendingvessel.

The second portion of the coked, stripped catalyst is transported to theregeneration zone. In the regeneration zone the coked catalyst undergoesregeneration by combustion of coke on the surface of the catalystparticles by contact with an oxygen-containing gas. Theoxygen-containing gas enters the bottom of the regenerator and passesthrough a dense fluidizing bed of catalyst. Flue gas consistingprimarily of CO₂ and perhaps containing CO passes upwardly from thedense bed into a dilute phase of the regenerator. A separator, such ascyclones or other means, remove entrained catalyst particles from therising flue gas before the flue gas exits the vessel through an outlet.Combustion of coke from the catalyst particles raises the temperaturesof the catalyst which is withdrawn from the regenerator and flowed to ablending vessel. Fluidizing gas Fluidizing gas passed into the blendingvessel contacts the catalyst and maintains the catalyst in a fluidizedstate to blend the recycled and regenerated catalyst.

The regenerated catalyst which is relatively hot is cooled by theunregenerated, coked catalyst which is relatively cool to reduce thetemperature of the regenerated catalyst by 28° to 83° C. (50° to 150°F.) depending upon the regenerator temperature and the coked catalystrecycle rate. The ratio of recycled catalyst to regenerated catalystentering the blending zone will be in a broad range from about 0.1 toabout 5.0 and more typically in a range from about 0.3 to about 3.0.Preferably, the blended catalyst will comprise a 1:1 ratio of recycledcatalyst to regenerated catalyst.

Regenerated catalyst from the regenerator will usually have atemperature in a range from about 677° to about 760° C. (1250° to 1400°F.) and, more typically, from about 699° to about 760° C. (1290° to1400° F.). The temperature of the recycled catalyst portion will usuallybe in a range from about 510° to about 621° C. (950° to 1150° F.). Therelative proportions of the recycled and regenerated catalyst willdetermine the temperature of the blended catalyst mixture that entersthe riser. The blended catalyst mixture will usually range from about593° to about 704° C. (1100° to 1300° F.).

Low hydrocarbon partial pressure operates to favor the production oflight olefins. Accordingly, the riser pressure is set at about 172 to241 kPa (25 to 35 psia) with a hydrocarbon partial pressure of about 35to 172 kPa (5 to 25 psia), with a preferred hydrocarbon partial pressureof about 69 to 138 kPa (10 to 20 psia). This relatively low partialpressure for hydrocarbon is achieved by using steam as a diluent to theextent that the diluent is 10 to 55 wt-% of feed and preferably about 15wt-% of feed. Other diluents such as dry gas can be used to reachequivalent hydrocarbon partial pressures.

The temperature of the cracked stream at the riser outlet will be about510° to 621° C. (950° to 1150° F.). However, we have found that riseroutlet temperatures above 566° C. (1050° F.) make more dry gas and moreolefins. Whereas, riser outlet temperatures below 566° C. (1050° F.)make less ethylene and propylene. Accordingly, it is preferred to runthe FCC process at a preferred temperature of about 566° C. to about630° C., preferred pressure of about 138 kPa to about 240 kPa (20 to 35psia). Another condition for the process is the catalyst to oil ratiowhich can vary from about 5 to about 20 and preferably from about 10 toabout 15.

Although, as stated, the feed is normally introduced into the risersection of the FCC zone, it is also within the scope of the presentinvention that the effluent from the pre-treatment zone is introducedinto the lift section of the FCC reactor. The temperature in the liftsection will be very hot and range from about 700° C. (1292° F.) toabout 760° C. (1400° F.) with a catalyst to oil ratio of about 100 toabout 150. It is anticipated that introducing the oil feed into the liftsection will produce considerable amounts of propylene and ethylene.

The following examples are presented in illustration of this inventionand are not intended as undue limitations on the generally broad scopeof the invention as set out in the appended claims.

EXAMPLE

Catalytic cracking of soybean oil was tested using an advanced crackingevaluation pilot plant. A commercial fluid catalytic catalyst from W.R.Grace, Inc. was used. The soybean oil was obtained from Aldrich ChemicalCo. and the gas and liquid hydrocarbon products were analyzed by gaschromatography. The analyses did not include oxygen balance nor wateranalysis. The reaction was run at 538° C. (1000° F.) at a catalyst:oilratio of 3:1 and a WHSV (hr⁻¹) of 3 hr⁻¹.

Based on these data, calculations were carried out to determineconversion at more severe conditions which are a temperature of 565° C.(1050° F.), a catalyst:oil ratio of 10/1 and 10% steam.

The actual and calculated conversions are presented below.

Actual and Calculated Cracking Conversions for Soybean Oil ComponentActual (%) Calculated (%) C2 & Methane 1.9 12.8 C3 5.4 24.5 C4 6.6 13.5gasoline 45.4 23.0 LCO¹ 11.4 5.0 CSO² 13.1 3.0 coke 4.5 6.5 water 11.7(estimate) 11.7 ¹LCO is light cycle oil which boils between 220-343° C.²CSO is clarified slurry oil which boils between 343 and 538° C.

1. A process for the catalytic cracking of a feedstock comprising apetroleum fraction and a non-petroleum fraction comprising firsttreating the feedstock in a pretreatment zone at pretreatment conditionsto remove at least a portion of contaminants present in the feedstockand produce an effluent stream; flowing the effluent from thepretreatment zone to a fluid catalytic cracking zone where the effluentis contacted with a cracking catalyst at cracking conditions to providea product stream comprising C₂-C₅ olefins and hydrocarbons wherein thepretreatment step is selected from the group consisting of contactingthe feedstock with an acidic ion exchange resin or contacting thefeedstock with an acid solution.
 2. The process of claim 1 where thecracking conditions include a temperature of about 566° C. (1050° F.) toabout 630° C. (1166° F.), a pressure of about 138 kPa (20 psia) to about240 kPa (35 psia) and a catalyst to oil ratio of about 5 to about
 20. 3.The process of claim 1 where the effluent is injected into the liftsection of the fluid catalytic cracking zone.
 4. The process of claim 3where the temperature in the lift section varies from about 700° C.(1292° F.) to about 760° C. (1400° F.).
 5. The process of claim 1wherein the non-petroleum fraction is selected from the group consistingof canola oil, corn oil, soy oil, rapeseed oil, soybean oil, colza oil,tall oil, sunflower oil, hempseed oil, olive oil, linseed oil, coconutoil, castor oil, peanut oil, palm oil, mustard oil, cottonseed oil,inedible oils, inedible tallow, yellow and brown greases, lard, trainoil, fats in milk, fish oil, algal oil, sewage sludge, pyrolysis oil,oxygenated liquids derived from the gasification of coal, oxygenatedliquids derived from depolymerization, synthetic oils, and mixturesthereof.
 6. The process of claim 5 where the inedible oil is jatrophaoil.
 7. A process for the catalytic cracking of a feedstock comprising apetroleum fraction and a non-petroleum fraction comprising firsttreating the non-petroleum fraction in a pretreatment zone atpretreatment conditions to remove at least a portion of contaminantspresent in the non-petroleum fraction and produce a purifiednon-petroleum stream; mixing the purified non-petroleum stream with apetroleum fraction to provide a feedstock; flowing the feedstock to afluid catalytic cracking zone where the feedstock is contacted with acracking catalyst at cracking catalyst at cracking conditions to providea product stream comprising C₂-C₅ olefins and hydrocarbons; wherein thepretreatment step is selected from the group consisting of contactingthe non-petroleum fraction with an acidic ion exchange resin orcontacting the non-petroleum fraction with an acid solution.
 8. Theprocess of claim 7 where the cracking conditions include a temperatureof about 566° C. (1050° F.) to about 630° C. (1166° F.), a pressure ofabout 138 kPa (20 psia) to about 240 kPa (35 psia) and a catalyst to oilratio of about 5 to about
 20. 9. The process of claim 7 where theeffluent is injected into the lift section of the fluid catalyticcracking zone.
 10. The process of claim 9 where the temperature in thelift section varies from about 700° C. (1292° F.) to about 760° C.(1400° F.).
 11. The process of claim 7 wherein the non-petroleumfraction is selected from the group consisting of canola oil, corn oil,soy oil, rapeseed oil, soybean oil, colza oil, tall oil, sunflower oil,hempseed oil, olive oil, linseed oil, coconut oil, castor oil, peanutoil, palm oil, mustard oil, cottonseed oil, inedible oils, inedibletallow, yellow and brown greases, lard, train oil, fats in milk, fishoil, algal oil, sewage sludge, pyrolysis oil, oxygenated liquids derivedfrom the gasification of coal, oxygenated liquids derived fromdepolymerization, synthetic oils, and mixtures thereof.
 12. The processof claim 11 where the inedible oil is jatropha oil.